import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner num = new Scanner(System.in);
        int n = num.nextInt();
        int odd = 0;
        int even = 0;
        for (int i = 1; i <= n; i++) {
            if(i%2 == 1){
                odd += i;
            }else{
                even -= i;
            }
        }
        int sum = odd+even;
        System.out.println(sum);
    }
}
